This project investigates multimodal compensatory plasticity in animals with early blindness , i.e. the capacity of the brain to reorganize itself when visual function is impaired after birth; functions that are normally carried out by one sense may be partly taken over by other senses. We are studying lid-sutured cats and blinded mice to test their somatosensory or auditory functions with behavioral, anatomical, and physiological methods. As a sign of somatosensory compensation, we have found that visually deprived cats have longer facial vibrissae than sighted cats. These vibrissae, are used for spatial discrimination, and help blind cats compensate for loss of vision in certain tasks. The same whisker growth observed in lid-sutured cats is found in mice if both eyes are removed after birth. The anatomical whisker representation in the somatosensory cortex of these mice, the "barrel field", is expanded by about one third, as shown with cytochrome oxidase and Nissl staining as well as with glutamic acid decarboxylase (GAD) immunohistochemistry. Auditory compensation of early blindness can be demonstrated for lid-- sutured cats in two ways. Behaviorally, these cats can perform sound localization more accurately than normal cats. Neurophysiologically, many more neurons are found in the superior colliculus of the midbrain tectum which respond to auditory stimuli. The same is true for a region of parietal cortex, the anterior ectosylvian area (AES), which provides a major source of cortical input to the tectum. A part of AES which is normally purely visual is taken over by auditory and somatosensory inputs in visually deprived cats. In addition, the spatial resolution of auditory neurons for sounds presented in different locations ("spatial tuning") is significantly sharper in such animals.